On Feb. 1, the Centers for Disease Control and Prevention issued a mask mandate for public transportation in the United States.

The federal agency’s order followed the lead of President Biden’s executive order on Jan. 20, his first day in office. The CDC’s rule requires most people to wear face masks “over the mouth and nose” while traveling on “conveyances into and within the United States.” It also states that “conveyance operators” must “use best efforts” to keep those masks strapped on.